The present invention relates to catheters for placement in body conduits where there is a necessity to provide a continuous flow of body fluids past the catheter. The invention particularly relates to coronary dilation catheters for use in administering treatments to widen a constricted blood flow passage frequently caused by a stenosis in, for example, a heart valve or coronary artery.
A stenosis is a region of a blood vessel which has been narrowed to such a degree that blood flow is restricted. If the stenosis is severe, treatment is required to restore adequate blood flow and often such treatment requires surgery or angioplasty. Transluminal angioplasty is a procedure for treating a patient having a stenosis or constricted region in a coronary artery. Frequently the stenosis can be expanded so that the artery will permit an acceptable blood flow rate.
Coronary angioplasty includes the insertion of a balloon through a patient's artery to the arterial stenosis and injecting a suitable fluid into the balloon to inflate it and hence expand the stenosis radially outwardly and compress it against the artery wall. Angioplasty has become a successful alternative to coronary arterial bypass surgery. The stenosis is compressed radially outward against the arterial wall to increase the cross-sectional serves area of the artery so that the artery has an acceptable blood flow rate.
Ordinary balloon catheters have a balloon fastened around the exterior of a hollow catheter tube. A tubular shaft is fastened to the balloon and the balloon is in fluid flow relation with the interior of the shaft. The shaft provides a fluid supply for inflating the balloon.
Coronary dilation catheters previously used in coronary angioplasty have the disadvantage of completely occluding the flow of blood while the balloon is expanded in the artery. However complete occlusion of a coronary artery cannot be permitted for any significant time without incurring serious risk of damage to portions of the heart that must receive blood from the occluded artery. Thus the balloon is pressurized for only a short time before it is depressurized to permit resumption of blood flow through the region of the stenosis. The inflation durations currently used are limited and can range from 15 seconds to 3 minutes, depending on the patient being treated. The limited inflation time frequently is not sufficient to treat a stenosis and inflations must be repeated.
Further, even if the arterial lumen is successfully dilated the effect may be only temporary. Restenosis of the artery after treatment is not uncommon. The sustained inflation of the balloon catheter, rather than short multiple inflations, reduces the possibility of post treatment restenosis and other clinical abnormalities.